pg_export_snapshot函数

psql (14.3)
Type "help" for help.

postgres=# \df+ pg_export_snapshot
List of functions
Schema | Name | Result data type | Argument data types | Type | Volatility | Parallel | Owner | Security | Access privileges | Language | Source code | Description
------------+--------------------+------------------+---------------------+------+------------+----------+----------+----------+-------------------+----------+--------------------+-------------------
pg_catalog | pg_export_snapshot | text | | func | volatile | unsafe | postgres | invoker | | internal | pg_export_snapshot | export a snapshot
(1 row)

postgres=# \c tt;
You are now connected to database "tt" as user "postgres".
tt=# begin TRANSACTION ISOLATION LEVEL REPEATABLE READ;
BEGIN
Time: 0.150 ms
tt=*# select * from t1 limit 10;
id | name
----+-----------
1 | 1_andyxi
2 | 2_andyxi
3 | 3_andyxi
4 | 4_andyxi
5 | 5_andyxi
6 | 6_andyxi
7 | 7_andyxi
8 | 8_andyxi
9 | 9_andyxi
10 | 10_andyxi
(10 rows)

Time: 0.529 ms
tt=*# select pg_export_snapshot(); ####查看当前快照
pg_export_snapshot
---------------------
00000004-00000118-1
(1 row)

Time: 0.290 ms

[postgres@harbor pg_snapshots]$ ls -la
总用量 8
drwx------ 2 postgres postgres 33 9月 12 11:30 .
drwx------ 20 postgres postgres 4096 9月 12 10:09 ..
-rw------- 1 postgres postgres 89 9月 12 11:30 00000004-00000118-1  ###当前快照在/pgccc/pgdata/pg_snapshots目录下可以查看。
[postgres@harbor pg_snapshots]$ pwd
/pgccc/pgdata/pg_snapshots
[postgres@harbor pg_snapshots]$

1.适用于REPEATABLE READ和SERIALIZABLE事务中。

2.在另一会话中我们可以导入这个快照。

tt=# BEGIN TRANSACTION ISOLATION LEVEL REPEATABLE READ ;
BEGIN
Time: 0.060 ms
tt=*# set transaction SNAPSHOT '00000004-0000011D-1';
SET
Time: 0.147 ms
tt=*# show tra
trace_notify trace_sort track_activity_query_size track_counts track_io_timing transaction_deferrable transaction_read_only
trace_recovery_messages track_activities track_commit_timestamp track_functions track_wal_io_timing transaction_isolation transform_null_equals
tt=*# show transaction_isolation
-#;
transaction_isolation
-----------------------
repeatable read
(1 row)

Time: 0.510 ms
tt=*# \q
[postgres@harbor pg_snapshots]$ ls -la
总用量 8
drwx------ 2 postgres postgres 33 9月 12 11:45 .
drwx------ 20 postgres postgres 4096 9月 12 10:09 ..
-rw------- 1 postgres postgres 89 9月 12 11:45 00000004-0000011D-1